4. Discussion
Our data indicate that the Matuyama-Brunhes transition boundary
constitutes 5.7 cm, between 7.1-12.8 cm depth of the sampled sedimentary
section, of the Za Hajovnou cave sediment. The magnetic reversal is
characterized and represented by frequent fluctuations of inclination
angle (Fig. 6a) and VGP latitude (Fig. 7a). We think that oscillations
in declination data show instability of the Earth’s magnetic field. On
the other hand, similar fluctuations which are seen in the previous
studies (Fig. 6) show the reliability of the data.
Although the data in this study and Okada et al. (2017) belong to
geographically different locations and sediment types, the similarity
during polar migration (Fig. 8) shows that the reversal was a dipole
transition, and the non-dipole field component was less significant (Oda
et al., 2000; Mochizuki et al., 2011; Simon et al., 2019).
In most of the samples with demagnetization generally at 20 mT, some
large fluctuations in the data may be considered as instability of
remanent magnetization. Although some samples (01_8M, 04_2M, 17_2M,
17_9M, 22_0M) are not demagnetized up to 100 mT, it shows that
minerals with low coercivity are responsible for the magnetization of
the cave sediments in our study. It can be clearly seen in the rock
magnetism measurements that the samples show similar behaviour during
the measurements that is maghemite in this case.
Note that most of the section contains samples from the polarity
transition. The data shows that the magnetic field was unstable for our
oldest sample already, when in reversed polarity. This observation goes
well with Yamazaki and Oda (2001) where they show the magnetic pole was
unstable long time before the actual reversal boundary and the magnetic
field started to fluctuate almost 150 cm deeper than the actual
transition (Fig. 7b, 10). We think that our data illustrate the same
instability, and this is why no paleomagnetic samples have VGP latitudes
that deviate less than 25° from the reversed position. We provide a more
detailed explanation of the reversed VGP behavior in our data that show
reversed polarity unrest well before the actual magnetic reversal.